关键词： GROUND state energy   CHEMICAL kinetics   CHEMICAL processes   MOLECULAR machinery (Technology)   ROTAXANES   ELECTRONIC apparatus & appliances  

摘要： The ability to design and confer control over the kinetics of the processes involved in the mechanisms of artificial molecular machines is at the heart of the challenge to create ones that can carry out useful work on their environment, just as Nature is wont to do. As one of the more promising forerunners of prototypical artificial molecular machines, chemists have developed bistable redox-active donor-acceptor mechanically interlocked molecules (MIMs) over the past couple of decades. These bistable MIMs generally come in the form of [2]rotaxanes, molecular compounds that constitute a ring mechanically interlocked around a dumbbell-shaped component, or [2]catenanes, which are composed of two mechanically interlocked rings. As a result of their interlocked nature, bistable MIMs possess the inherent propensity to express controllable intramolecular, large-amplitude, and reversible motions in response to redox stimuli. In this Account, we rationalize the kinetic behavior in the ground state fora large assortment of these types of bistable MIMs, including both rotaxanes and catenanes. These structures have proven useful in a variety of applications ranging from drug delivery to molecular electronic devices. These bistable donor-acceptor MIMs can switch between two different isomeric states. The favored isomer, known as the ground-state co-conformation (GSCC) is in equilibrium with the less favored metastable state co-conformation (MSCC). The forward (k(f)) and backward (k(b)) rate constants associated with this ground-state equilibrium are intimately connected to each other through the ground-state distribution constant, K-GS. Knowing the rate constants that govern the kinetics and bring about the equilibration between the MSCC and GSCC, allows researchers to understand the operation of these bistable MIMs In a device setting and apply them toward the construction of artificial molecular machines. The three biggest influences on the ground-state rate constants arise fr

关键词： NONLINEAR dynamical systems   MECHANICAL engineering   FRICTION   STRUCTURAL mechanics   EQUILIBRIUM   VIBRATION measurements  

摘要： Real applications in structural mechanics where the dynamic behavior is linear are rare. Usually, structures are made of components assembled together by means of joints whose behavior maybe highly nonlinear. Depending on the amount of excitation, joints can dramatically change the dynamic behavior of the whole system, and the modeling of this type of constraint is therefore crucial for a correct prediction of the amount of vibration. The solution of the nonlinear equilibrium equations by means of the Harmonic Balance Method (HBM) is widely accepted as an effective approach to calculate the steady-state forced response in the frequency domain, in spite of Direct Time Integration (DTI). The state-of-the-art contact element used to model the friction forces at the joint interfaces is a node-to-node contact element, where the local contact compliance is modeled by means of linear springs and Coulomb's law is used to govern the friction phenomena. In the literature, when the HBM is applied to vibrating systems with joint interfaces and the state-of-the-art contact model is used, an uncoupled approach is mostly employed: the static governing equations are solved in advance to compute the pre-stress effects and then the dynamic governing equations are solved to predict the vibration amplitude of the system. As a result, the HBM steady-state solution may lead to a poor correlation with the DTI solution, where static and dynamic loads are accounted for simultaneously. In this paper, the HBM performances are investigated by comparing the uncoupled approach to a fully coupled static/dynamic approach. In order to highlight the main differences between the two approaches, a lumped parameter system, characterized by a single friction contact, is considered in order to show the different levels of accuracy that the proposed approaches can provide for different configurations. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： 挖掘机   动力学   工作装置  

摘要： 机械式挖掘机工作装置的动力学研究是从挖掘机的理论动力特性曲线出发,以极端工况为计算条件,以工作装置的提升和推压系统的自然系统作为计算模型;将斗柄、动臂视为弹性体,运用拉格朗日方程建立9自由度工作装置的弹性动力学数学模型,有别于以往的刚体动力学模型;采用振型叠加法求得位移响应及各构件的最大动载荷及动载荷系数。研究中提出的挖掘机动力学分析方法,可适用于设计挖掘机新产品时的动力计算和强度校核,也可用于已有产品的动力评价。

关键词： 机械   减震   汽车  

摘要： 减震技术的核心是消除干扰性振动或找出解决的方法，因外部条件的不同，对减振器的使用要求也会相应的不同。在不同的国家或不同的地区，他们各自的天气环境、道路建筑等都有着很大的区别。单一的减振器是可能都满足他们的性能要求。

关键词： 铁水预处理   机械搅拌法   脱硅   动力学   研究  

摘要： 在实验室进行了模拟铁水预处理机械搅拌法脱硅的动力学试验,考察了铁水温度、搅拌方法、初始硅含量、脱硅渣碱度等因素对脱硅反应速率的影响.试验表明：铁水温度对脱硅速率影响较小;机械搅拌可显著提高脱硅速率;脱硅反应初期的限制环节是硅在铁水侧的传质,当渣中FeO含量降低到一定程度后,FeO在渣相侧的传质成为脱硅过程的限制环节,或与硅在铁水侧的传质共同控制速度;脱硅渣碱度在0.32 ～0.65变化对脱硅速率无显著影响.

关键词： greenhouse cooling   fan ventilation   roof ventilators   combined ventilation  

摘要： The aim of this study was to analyse air exchange and temperature distribution in a greenhouse with combined mechanical and natural ventilation and to design more efficient mechanical ventilation *** this purpose,a computational fluid dynamics(CFD)model of the greenhouse was *** configurations were considered:Configuration 1(mechanical ventilation and closed roof ventilators),Configurations 2 and 3(mechanical ventilation and roof ventilators open 30%and 100%,respectively).After validation,the CFD model was used to improve the design of the greenhouse mechanical ventilation system in each of the three configurations *** greenhouse lengths,28 m,50 m,75 m and 100 m,were used in the *** to fan ventilation only,roof ventilation improved the climate of fan-ventilated greenhouses in terms of the air exchange rate(22%)and climate uniformity because the internal air was mixed better than with mechanical ventilation *** the greenhouse length increased,more advantages were achieved with natural ventilation compared to mechanical *** most configurations,there was a strong linear correlation between temperature gradient and greenhouse *** greenhouse whose regression line had the steepest slope was the one with closed roof *** the fan capacity produced a general reduction in temperature,but the effect was less intense for the greenhouses with open roof *** to box inlet ventilators,an enlarged continuous inlet in the wall opposite the fans increased overall system performance because it eliminated backflow recirculation zones,which are prone to produce high temperatures.

关键词： 真空机械手   运动学   牛顿-欧拉法   动力学仿真  

摘要： 根据FROG-LEG型真空机械手的结构特点,提出了其等效的串联结构运动学模型,并求出了运动学的正反解。将FROG-LEG型真空机械手动力学问题分为水平和垂直两个方向进行讨论,用牛顿-欧拉法求出了两个方向的动力学方程。最后利用MATLAB机器人工具箱对机械手的运动学和动力学特性进行了仿真实验。

关键词： 工程机械   产品   约翰迪尔   董事长   代表团   委员会  

摘要： 1976年，公司董事长威廉·休伊特（William Hewitt）率美中贸易全国委员会代表团首次访华，奠定了约翰迪尔在中国发展的基础。

关键词： 机械制造   转型升级   天津市   公司   有限   压力   纪实   加工企业  

摘要： 坐落于宝坻区朝霞街道工业区的天津宝洪源机械制造有限公司始建于1994年，当时仅为一家拥有两台车床的加工小作坊，经过一路摸索打拼，逐渐发展到今天的规模。作为一家科技型加工企业，宝洪源的产品涉及工程机械、船舶设备、风力发电设备、钢结构等领域，2013年公司销售收人超亿元。谈起企业的转型升级经历，企业负责人感慨万千。

关键词： Adenosine Triphosphate/metabolism   Hydrolysis   Kinesin/metabolism   Kinetics   Microtubules/metabolism   Models, Biological   Probability  

摘要： Motivation: Kinesin is a smart motor protein that steps processively forward and backward along microtubules (MTs). The mechanical kinetics of kinesin affecting its stepping behavior is not fully understood. Here, we propose a mathematical model to study the mechanical kinetics of forward and backward stepping of kinesin motor based on the four-state discrete stochastic model of the motor. Results: Results show that the probabilities of forward and backward stepping can be modeled using the mean probabilities of forward and backward kinetic transitions, respectively. We show that the backward stepping of kinesin motor starts when the probability of adenosine diphosphate (ADP) binding to the motor is much higher than that of adenosine triphosphate (ATP) binding. Furthermore, our results indicate that the backward stepping is related to both ATP hydrolysis and synthesis with rate limiting factor being ATP synthesis. Low rate of ATP synthesis under high backward loads above 10 pN is also suggested as a reason for the detachment of kinesin motor from MT in the kinetic state ***.P-i.